1. Field of the Invention
This invention relates to an automobile seat occupant sensor and airbag control for detecting the location and weight of a person in car seat, and in particular to a sensor that can detect the presence and location of an occupant using strain sensitive resistors and provide an electrical signal to control activation of an airbag.
2. Description of the Related Art
Various devices are well known for their ability to measure force, pressure, acceleration, temperature, position, etc. by using a sensing structure combined with signal processing electronics. One general type of sensor or transducer for such applications is a resistive strain gauge sensor in which force or pressure is sensed or measured based on strain placed on the resistors. Resistive strain gauges function by generating changes in resistance proportional to force which causes dimensional changes of the resistor.
Many types of strain gauge sensors have been designed and made commercially available. Various strain gauge sensors have proven to be generally satisfactory. Prior art sensors; however, have tended to be rather expensive and not suitable in certain applications such as sensing the presence of an occupant in an automobile seat. A sensor suitable for such an application must be compact, robust, impervious to shock and vibration and yet inexpensive.
Automobile seats can use sensors to activate air bags, which would be deployed during an accident. Injury to infants or small children from air bag deployment with excessive force is a current industry problem. A weight sensor in the seat can be used to control the deployment force during air bag activation. If a heavy person is in the seat, the airbag is deployed at full force. If a light person is in the seat, such as a child, the airbag is deployed at a slower, less forceful rate.
Another problem with airbag deployment is determining the position and posture of a person in a vehicle seat. If the seat occupant is located in the front of the seat, it is desired to activate the air bag with less force. If the seat occupant is located in the rear of the seat, it is desired to activate the air bag with more force. Similarly, if the seat back is an automobile seat is reclined, it may be desired to control the activation of the airbag based upon the seat back angle. For example, if the seat back is reclined fully, it may be desired to activate the air bag with more force. If the seat back is in an upright position, it may be desired to activate the airbag with less force.
U.S. Pat. No. 5,573,269 discloses a system that uses multiple sensors. Several weight sensors are placed in the seat, the floor and a seat angle sensor is attached to the seat back. This system has many disadvantages. It is expensive to produce and install all the sensors. The weight sensor in the seat is attached to the springs which can give inaccurate readings of weight depending on the placement of the sensors in the seat.
Other seat occupant detection systems have been devised based upon ultrasonic sensing technologies. The occupants distance from the dashboard is measured by a sensor. Other sensors try to measure the size of the occupant. Unfortunately, the ultrasonic systems produce frequent errors in calculating the size of the occupant as they have difficulty in interpreting an occupant shifting in the seat, moving the seat forward or backward and reclining the seat.
A current unmet need exists for a reliable, low cost, simple and robust automobile seat weight sensor and system that is used to control airbag deployment. A current unmet need also exists for an air bag control system that can monitor occupant weight, seat position and seat back angle with a minimum number of sensors at a low cost.
3. Related Art
Examples of patents that are related to the present invention are as follows, and each patent is herein incorporated by reference for the supporting teachings:
U.S. Pat. No. 5,573,269 is a apparatus for sensing and restraining an occupant of a vehicle seat.
U.S. Pat. No. 4,556,598 is a porcelain tape for producing porcelainized metal substrates.
U.S. Pat. No. 5,232,243 is an occupant sensing apparatus.
U.S. Pat. No. 5,276,432 is a patient exit detection mechanism for hospital bed.
U.S. Pat. No. 5,739,757 is an vehicle passenger weight sensor.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging the applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, the applicant's claimed invention.